Today the "relative gene
expression approach" is increasingly used in gene expression
studies, where the expression of a target gene is standardised by a non-regulated
reference-gene or by an index, containing more
reference-genes. Several mathematical algorithm have been developed to compute the
expression ratio, based on real-time PCR efficiency and the crossing point (Ct or CP)
deviation (=> delta CP) of an unknown sample versus a control. But
all
published equations and
available models for the calculation of relative expression ratio
allow only for the determination of a single
transcription difference
between one control and one sample.